A cardinal rule in mass spectrometry is that the mass spectrum should not be acquired during a time segment in which the partial pressure of the analyte is changing. This rule would seem to preclude the successful use of GC-MS as the very definition of a gas chromatogram is a change in analyte partial pressure with time. The rule was designed to protect the integrity of the pattern of relative peak intensities in the mass spectrum which are critical for compound identification, and are the fundamental basis for library search routines in identifying unknown mass spectra. The extent to which the problem of spectral skewing exists in modern GC-MS applications is being assessed with the use of three different mass analyzers: quadrupole, ion trap, and time-of-flight analyzer. In all cases, capillary column chromatographs are interfaced to the mass analyzer in an effort to present analytes to the mass spectrometer in a challenging exhibition of dynamic changes in analyte concentration. The GC time-of-flight instrument is equipped with an integrating transient recorder which will permit the concept of time array detection to be used to acquire mass spectra at a rate of 100 to 1000 hertz.